Method and device for determining fibre orientation in a paper sample

ABSTRACT

The invention relates to a method and device for determining fiber orientation in a paper sample. The surface of the sample ( 1 ) is illuminated from an oblique angle ( 11 ) by means of more than one light source ( 2, 3 ). The illumination is rotated on the surface of the sample by electronically switching the light sources on and off in turn by means of a switch ( 12 ). The intensity of the light reflected from the surface of the sample is measured using at least one sensor ( 5 ) and, based on the measured light intensity and momentary direction of illumination, the fiber orientation in the sample is determined by means of a computing device ( 13 )

CROSS REFERENCE TO RELATED APPLICATION

The present application is the U.S. national stage application ofInternational Application PCT/FI99/00544, filed Jun. 21, 1999, whichinternational application was published on Dec. 29, 1999 asInternational Publication WO 99/67625 in the English language. TheInternational Application claims the priority of Finnish PatentApplication 981443, filed Jun. 23, 1998.

BACKGROUND OF THE INVENTION

The present invention relates to a method as defined in the claims andto a device as defined in the claims for determining fiber orientationin a paper sample.

In this context ‘paper sample’ refers to web-like products, such aspaper, cardboard or other paper industry products, manufactured fromlignocellulose based materials.

‘Fiber orientation’ refers to the orientation of the fibers in a papersample. The fibers are mostly oriented in the machine direction ratherthan in the transverse direction. In a paper sample, the degree andangle of fiber orientation vary in relation to the web width, i.e. inthe transverse direction of the paper web, and in relation to time, i.e.in the longitudinal direction of the paper web. Fiber orientation isgenerally different in different paper sorts.

Previously known is a method for determining the mean fiber orientationin a paper sample as a ratio of machine direction tensile strength totransverse direction tensile strength, i.e. as a strength ratio.Further, a method for determining mean orientation by measuring thespeed of propagation of ultrasound in a web in different directions isknown. In this method, the distance lag or sound modular ratio obtainedindicates the mean orientation angle and degree. Devices suited forimplementing the method are manufactured e.g. by Lorentzen & Wettre andNomura.

Previously known is also a method for determining mean orientation byoptical means. In the method, a thin round beam of light is directed atthe paper surface and the shape of the beam is measured from the otherside of the paper. The ellipticity of the shape of the beam increases inproportion to the degree of orientation in the sample. Instruments forthis purpose are manufactured e.g. by Honeywell.

A problem with the prior-art methods is that only the mean fiberorientation in a certain area in the paper sample can be determined.Prior-art methods for determining fiber orientation are difficult to usein practice; for instance, the tensile strength ratio is not easy todetermine. Tensile strength ratio is not a good measure of fiberorientation in other respect, either, because, in addition to fiberorientation, it depends on the drying history of the paper, such as thedegree of shrinkage occurring in the web as it is drying.

A further problem is that prior-art methods are not applicable for thedetermination of surface orientation (surface orientation refers tofiber orientation at the paper surface) and surface orientationdifference between surfaces.

However, determination of surface orientation is an important functionbecause, depending on the former type used in the paper machine and onthe grammage level of the paper web, the web may have a significantorientation difference between its surfaces. This is a problemespecially in multi-layer type web formation, in which the layers of theweb are produced using different head boxes/formers or a multi-channelhead box. Moreover, a surface orientation difference can be clearlyobserved in paper produced using conventional head box—formercombinations or dilution head boxes. For example, in fine grade paperand sheeted printing paper, a surface orientation difference andvariations of orientation in different areas of the paper surface maycause severe curling of the sheet, which again may result in toppling ofpaper piles, among other things.

SUMMARY OF THE INVENTION

The object of the invention is to eliminate the problems mentioned aboveand to disclose a new workable method and device for determining fiberorientation that will be easier to implement in industrial applications.A further object of the invention is to disclose a method and device fordetermining, besides mean fiber orientation, fiber orientationseparately for the upper and/or lower surfaces of a paper sample.

The method and device of the invention are characterized by what ispresented in the claims.

The invention is based on determining fiber orientation in a papersample.

According to the invention, the surface of the sample is illuminatedfrom an oblique angle using more than one light source. The illuminationis rotated on the surface of the sample by switching the light sourceselectronically on and off in turn by means of a switch. The intensity ofthe light reflected from the sample surface is measured by means of atleast one sensor and, based on the measured light intensity andmomentary direction of illumination, fiber orientation in the sample isdetermined using a computing device.

Based on the measured light intensity and the momentary direction ofillumination, it is possible to determine the directional angle and/ordegree of fiber orientation in the sample. The surface of the sample canbe illuminated and/or the intensity of the light reflected from thesample surface can be measured continuously.

In an embodiment of the invention, the surface of the sample isilluminated using LED type light sources. If desirable, the sample canbe illuminated with polarized or non-polarized light.

In an embodiment of the invention, the intensity of the light reflectedfrom the surface of the sample is measured using a light emitting diode.The light emitting diode is disposed e.g. substantially perpendicularlyto the sample surface. In an embodiment, at least two sensors aredisposed substantially in the form of a bar, and the bar is placed in aposition substantially perpendicular to the direction of motion of thesample.

In an embodiment of the invention, the light sources and sensor aredisposed in a substantially unitary assembly, forming a measuringdevice. In an embodiment, the device comprises a movable controllingelement, the measuring device being placed substantially in conjunctionwith said controlling element. The measuring device as such may be freeof movable parts. The controlling element may be designed to be movableby a previously known technique, e.g. using a hydraulic device.

According to an embodiment, the measurement is performed substantiallyabove and below the sample. In an embodiment of the invention, thesample is a moving web.

With the method and/or device of the invention, fiber orientation ondifferent surfaces of the sample can be determined separately so that itwill be possible to determine separate surface orientations and asurface orientation difference in addition to the mean fiberorientation. A further advantage of the invention is that it allowson-line type determination of fiber orientation even from a movingsample and without breaking the sample.

A further advantage is an insignificant need for maintenance of themeasuring device because the measuring device is completely or partiallyfree of movable parts. A further advantage is a compact size andsimplicity of manufacture of the device. The apparatus can be easilyadded to existing equipment e.g. in paper industry without anysubstantial changes, thus allowing easy, quick and advantageousimplementation of the method.

A further advantage of the invention is reproducibility and stability ofthe light intensity measured by the sensor.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

In the following, the invention will be described by the aid of detailedexamples of its embodiments with reference to the attached drawings,wherein

FIG. 1 presents an embodiment of the device of the invention in lateralview,

FIGS. 2 and 3 present embodiments of devices according to the inventionin top view,

FIG. 4 presents an embodiment of a device according to the invention,

FIG. 5 presents an on-line embodiment of a device according to theinvention, and

FIG. 6 presents a detail of the embodiment presented in FIG. 5.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 presents an embodiment of the apparatus of the invention for themeasurement of fiber orientation. In this embodiment, LED-type lightsources 2 and 3 are used. LED-type light sources can be turned on andoff very rapidly without substantial delays. The number of light sourcesis more than one, preferably at least three.

FIG. 1 shows further that the light sources illuminate the surface ofthe sample 1 from an oblique angle 11 of e.g. about 45 degrees. It isnaturally possible to illuminate the sample surface from angles of othersizes as well. The illuminating beam may typically have a smalldiameter, e.g. below 10 mm.

The sample in this embodiment is a moving paper web, from whose surfacethe light is reflected substantially perpendicularly in an upwarddirection. The angle of incidence of the light on the paper surface andthe angle of departure of the reflected light from the surface maydiffer from each other; for instance, the ratio of incidence angle todeparture angle is 45°/90°. The intensity of the light reflected fromthe surface is measured using at least one sensor 5, which in theembodiment in FIG. 1 is a light emitting diode, preferably disposedperpendicularly to the sample. The measurement is performed in ameasuring area having a diameter below 10 mm.

The surface of the sample 1 can be illuminated and/or the intensity ofthe light reflected from the sample surface can be measuredcontinuously.

FIG. 2 presents an embodiment of the disposition of the light sources 2,3 and 4 in relation to the sensor 5 as seen from above. The lightsources can be placed at equal distances in a circular arrangement onthe circumference of an imaginary circle e.g. so that the sensor remainsat the centre of the light sources in the middle of the circle. In apreferred case, the light sources can also be disposed in a semicirculararrangement on the circumference of an imaginary circle, e.g. asillustrated in FIG. 3, while the sensor is placed at the centre of theimaginary circle.

The illumination is rotated on the surface of the sample by turning thelight sources on and off successively by means of an electronic switch12 (FIG. 1). Since the turn-on time of especially LED-type light sourcesis very short, a high virtual speed of rotation is achieved withoutmovable parts as light rays proceeding from different directions, i.e.light sources, are turned on and off and the illumination substantiallyrotates around the spot on the sample surface observed by the sensor. Inthe device of the invention, it is possible to use any LED-type lightsources and electronic switches known in this field, the details ofwhich will not be described in this context.

As the light beam is rotated, the light falls on the sample surface fromdifferent directions, so it is reflected from the sample surface indifferent ways depending on the fiber orientation and the direction ofthe light directed at the fibers. Maximum reflection occurs when thelight falls on the fiber perpendicularly from a lateral direction.

In the embodiment in this example, the intensity of the light reflectedfrom the illuminated spot on the surface of a sample to which anilluminating beam is applied alternately from three directions ismeasured. On the basis of the measurement or series of measurements oflight intensity and the momentary direction of illumination, it ispossible to determine the directional angle and/or degree offiber/surface orientation. The determination of fiber/surfaceorientation can be performed on the basis of the measurement results byusing a separate computing device, which may be any known computingdevice 13 (FIG. 1) which will not be described here in detail.

To produce polarized light, a polarizing element 14 (FIG. 1), e.g. apolarization filter, may be placed in front of each LED-type lightsource 2 and 3. Other solutions for producing polarized light, such as alight source producing polarized light directly, can also be utilized inthe method. Naturally, nonpolarized light may be used as well.

FIG. 4 presents an embodiment of the device of the invention. In thisembodiment, the sensors 5 and 6 are mounted in pairs above and below thepaper sample 1, the first one 5 of the sensors being placed above thepaper sample and the second one 6 above it. The sensors are placedagainst the paper web 1 so that opposite sensors also form a support forthe paper web during the measurement, preventing the sample fromfluttering in the measuring gap. The sensors measure the surfaceorientation in both surfaces simultaneously. The sensors above and belowthe sample can be disposed in a stepped manner relative to each other inthe direction of motion of the sample as shown in the figure, so thatlight rays penetrating the paper will not disturb the measurement.

FIG. 5 shows an on-line embodiment of the device of the invention. Themeasuring device is mounted substantially in conjunction with a movablecontrolling element 15. In this embodiment, the sensor 5, light sources2, 3 and 4, electronic switch 12 and computing device 13 form asubstantially unitary measuring device. The measuring device maynaturally only consist of a sensor and/or light sources.

The measuring device in itself is preferably free of movable parts, thusreducing the need for maintenance.

In the embodiment in FIG. 5, the controlling element 15, held in ameasuring position, is brought close to the paper sample 1, which ismoving e.g. on a rigid cylinder 10 with a large diameter in a papermachine. In this embodiment, the measuring device does not come intocontact with the sample. The controlling element can be moved, in thisembodiment raised and lowered as necessary. The on-line embodiment ofthe device can be used to measure light intensity from a moving papersample, such as a web running in the wire section of a paper machine.

FIG. 6 presents a detail of FIG. 5. In the embodiment in FIG. 6, insteadof a single sensor 5, a sensor bar 8, i.e. a measuring device consistingof a number of sensor modules 7, i.e. sensors mounted side by side, isconnected to a controlling element 15. The sensor bar is so mounted onthe controlling element that the bar is substantially perpendicular tothe direction of motion of the sample 1. In this embodiment, the size ofthe sensor modules may be e.g. 50×100 mm. A sensor bar with sensormodules mounted on it can be used for continuous measurement of surfaceorientation profile across the whole width of a paper web, e.g. with aspacing of 50 mm, for instance to implement accurate monitoring of theeffects of adjustments of the headbox lip of the paper machine.

Each sensor module 7 may naturally comprise light sources, an electronicswitch and/or a computing device besides a sensor or sensors.Alternatively, for each sensor or sensor module on the bar, the sensorbar 8 may naturally be provided with a given number of light sources andother components of the device of the invention. Several sensor bars maybe used in conjunction with the device of the invention.

In the embodiment in FIG. 5, the intensity of the light reflected fromthe surface of the paper is measured from both sides of the web 1 usingtwo controlling elements 15 disposed on either side of the web, e.g.substantially in the vicinity of two successive rollers or cylinders sothat the first controlling element is above the web and the second onebelow it.

Results obtained using the method and device of the invention fordetermining fiber orientation have been compared with fiber orientationsdetermined using a commercial sound module measuring device. The resultsobtained indicate that the method of the invention and the previouslyknown method of determination correspond to each other.

Furthermore, reproducibility measurements performed on exactly the samespot have proved that the light intensity measured using a sensoraccording to the invention is reproducible and stable.

The method and device of the invention are applicable as differentembodiments for the determination of any fiber orientation, especiallysurface orientation in a paper web.

The embodiments of the invention may be varied within the scope of thefollowing claims.

What is claimed is:
 1. A method for determining fiber orientation in apaper sample comprising the steps of: providing a light sensor, thelight sensor being spaced from the sample and facing a surface of thesample to receive light from an area on the surface of the sample viewedby the light sensor; arranging a plurality of light sources incircumferentially spaced positions at least partially around the lightsensor, the light sources being radially spaced from the light sensorand being spaced from the sample; successively turning each of the lightsources on and then off to cause each of the light sources, in turn, tosequentially and obliquely project a beam of light from the light sourceonto the area on the sample, the arcuate spacing of the light sourcescausing the light beam of each of the sources to illuminate the areafrom a different direction, the successive turning on and off of thelight sources being at a common frequency in which a given light sourceis on while the other light sources are off and off while other lightsources are on, the successive, repetitive turning on and off of thelight sources at the common frequency creating a rotational effect inthe illumination of the area of the sample; receiving, with the lightsensor, a series of light signals comprising light obtained from thesample as a result of the sequential illumination of the area on thesample from different directions by the light projected from the lightsources, the properties of the obtained light signals being dependent onthe orientation of fibers in the sample and the direction ofillumination of the sample by each of the light sources; measuring aproperty of each of the received light signals; using the properties ofthe received light signals and the associated directions of illuminationto determine fiber orientation properties of the sample.
 2. Method asdefined in claim 1, characterized in that, in the method, at least oneof the directional angle and degree of fiber orientation in the sampleis determined.
 3. Method as defined in claim 1, characterized in thatthe surface of the sample is illuminated using LED-type light sources.4. Method as defined in claim 1, characterized in that the surface ofthe sample is illuminated substantially at an angle of about 45 degrees.5. Method as defined in claim 1, characterized in that the surface ofthe sample is illuminated by means of three light sources.
 6. Method asdefined in claim 1, characterized in that the light sources are disposedin a circular arrangement and surround the light sensor.
 7. Method asdefined in claim 1, characterized in that the light sources are disposedin a semicircular arrangement and partially surround the light sensor.8. Method as defined in claim 1, characterized in that the sample isilluminated with polarized light.
 9. Method as defined in claim 1,characterized in that the light obtained from the surface of the sampleis sensed by means of a light emitting diode.
 10. Method as defined inclaim 1, characterized in that the sensor is disposed in a substantiallyperpendicular position relative to the surface of the sample.
 11. Methodas defined in claim 1, characterized in that the paper sample is amoving web.
 12. A device for determining fiber orientation in a papersample comprising: a light sensor spaced from the sample and facing asurface of the sample to receive light from an area on the surface ofthe sample viewed by said light sensor; a plurality of light sourceslocated in circumferentially spaced positions at least partially aroundsaid light sensor, said light sources being radially spaced from saidlight sensor and being spaced from the sample; means for electronically,successively switching each of said light sources on and then off tocause each of said light sources, in turn, to sequentially and obliquelyproject a beam of light from the light source onto the area on thesample, the arcuate spacing of said light sources causing the light beamof each of said sources to illuminate the area from a differentdirection, the successive switching on and off of said light sourcesbeing at a common frequency in which a given light source is on whilethe other light sources are off and off while other light sources areon, the successive, repetitive switching on and off of said lightsources at the common frequency creating a rotational effect in theillumination of the area of the sample; said light sensor receiving aseries of light signals comprising light obtained from the sample as aresult of the sequential illumination of the area on the sample fromdifferent directions by the light projected from said light sources, theproperties of the obtained light signals being dependent on theorientation of fibers in the sample and the direction of illumination ofthe sample by each of said light sources; and means coupled to saidlight sensor for determining fiber orientation properties of the samplefrom the properties of the received light signals and the associateddirections of illumination.
 13. Device as defined in claim 12,characterized in that the light sources are LED-type light sources. 14.Device as defined in claim 12, characterized in that the angle (11) ofillumination of the light sources is substantially about 45 degrees. 15.Device as defined in claim 12, characterized in that the devicecomprises three light sources.
 16. Device as defined in claim 12,characterized in that the light sources are disposed in a circulararrangement and surround said light sensor.
 17. Device as defined inclaim 12, characterized in that the light sources are disposed in asemicircular arrangement and partially surround said light sensor. 18.Device as defined in claim 12, characterized in that the devicecomprises a polarizing element disposed substantially in conjunctionwith at least one of the light sources.
 19. Device as defined in claim12, characterized in that said light sensor is a light emitting diode.20. Device as defined in claim 12, characterized in that the devicecomprises at least two devices disposed substantially side by side inthe form of a bar.
 21. Device as defined in claim 12, characterized inthat the light sources and said light sensor are disposed in asubstantially unitary assembly forming a device so that the light sensoris substantially perpendicular to the surface of the sample.
 22. Deviceas defined in claim 12, characterized as including a movable controllingelement (15), the device for determining fiber orientation beingdisposed substantially in conjunction with said controlling element. 23.Device as defined in claim 12, characterized in that the device issubstantially free of movable parts.
 24. Device as defined in claim 12,characterized in that the device is a continuously operating device. 25.Method as defined in claim 1 characterized in that at least one of thestep of successively turning the light sources on and off and the stepof receiving the light signals is carried out continuously.
 26. Methodas defined in claim 11 characterized as carrying out the steps of themethod at a plurality of locations arranged in a direction transverse tothe direction of movement of the web.
 27. Method as defined in claim 1wherein the paper sample has a pair of surfaces and wherein the steps ofthe method are carried out for both surfaces of the paper sample.